Flycatchers to European Starling (pg 1; updated 15 Oct 2012)
Warblers through House Sparrow + Literature Cited (below; updated 15 Oct 2012)
Bill tumors, most due to avian pox (pg 3; not being updated)
This compilation of bill deformities is property of the Rouge River Bird Observatory. Do not use or cite without written permission.
Warblers through House Sparrow
| Species | Details | Source |
|---|---|---|
| Ovenbird (Seiurus aurocapilla) | Photo dated 5 Oct 2008; U-U; Edinburg, NY; maxilla curved down at tip, mandible missing or unhinged-looking, pointing downward at a steep angle | Grant Leavitt on Flickr |
| Worm-eating Warbler (Helmitheros vermivorum) | Sept 2007; Walls of Jericho, Jackson Co., AL; maxilla elongated | Elliot Schunke,(ewschunke AT hotmail.com) |
| Northern Waterthrush (Parksia noveboracensis) | 30 April 2007; AHY-U; Dearborn, Wayne Co., MI; maxilla bill eroded and shortened, perhaps healed pox (cross referenced in bill tumor table) | Rouge River Bird Observatory,Julie Craves (jac.rrbo AT gmail.com) |
| Black-and-white Warbler (Mniotilta varia) | 12 Sep 1989; HY-M; Rector, PA; maxilla crossed right, due to injury? | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Prothonotary Warbler (Protonotaria citrea) | 13 Oct 2012; HY-F; Key Biscayne, FL; maxilla elongated, mandible split with each side curving inward | Robin Diaz (rd4birds AT bellsouth DOT net) |
| Tennessee Warbler (Oreothlypis peregrina) | 25 Sep 1977; HY-U; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol.com) |
| Tennessee Warbler | 15 Oct 2005; HY-U; near Amherstberg, Ontario; maxilla twisted and short, overlapping mandible | Holiday Beach Migration Observatory |
| Nashville Warbler (Oreothlypis ruficapilla) | 6 Nov 1974; HY-F; Rector,PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol.com) |
| Nashville Warbler | 19 May 1997; SY-U; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Mourning Warbler (Geothlypis philadelphia) | 18 Sep 03; HY-F; Burdett,NY; crossed, maxilla shorter than bottom | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Common Yellowthroat (Geothlypis trichas) | 12 Sep 1984; HY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Common Yellowthroat | Northampton Co., VA, fall 1998 | Larry Robinson (LarryRob aT aol.com) |
| Common Yellowthroat | 8 Aug 2003; HY-M; Burdett, NY; entire bill missing back to nares - appears chewed | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Common Yellowthroat | 1 Sep 2003; HY-M; Burdett, NY; crossed, mandible short | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Common Yellowthroat | 19 May 2008; AHY-M; near Oahe Dam, Stanley Co., SD; slightly crossed and did not close properly | Doug Backlund (Doug.Backlund AT state.sd.us) |
| Hooded Warbler (Setophaga citrina) | Female; Apopka, FL | Clay Black (clay.black AT swfwmd.state.fl.us) |
| Hooded Warbler | 5 Oct 1969; HY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Hooded Warbler | HY-M; 6 Sep 2003; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Hooded Warbler | HY-M; 10 Sep 2003; Rector, PA; shriveled end of maxilla | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| American Redstart (Setophaga ruticilla) | 12 Sep 1971; HY-F; Rector, PA; maxilla crossed right | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Cape May Warbler (Setophaga tigrina) | 27 Sep 1974; HY-F; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Cape May Warbler | 27 Spe 1975; HY-F; Rector, PA; slightly crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Cape May Warbler | 5 Oct 1984; HY-F; Rector, PA; maxilla crossed right | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Yellow Warbler (Setophaga petechia) | Alberta, Canada | (gmbooth AT telusplanet.net) |
| Yellow Warbler | 26 May 1997; SY-F; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Chestnut-sided Warbler (Setophaga pensylvanica) | 10 Sep 2006; HY-U; both mandible and maxilla tips bent slightly left (like Wrybill); Metro Beach Metropark, Macomb Co., MI | Allen Chartier (amazilia1 AT comcast.net) |
| Blackpoll Warbler (Setophaga striatus) | 21 Sep 1986; HY-F; Rector, PA; maxilla crossed left | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Black-throated Blue Warbler (Setophaga caerulescens) | 26 Oct 2004; HY-F; Key Biscayne, FL; maxilla crossed over mandible | Robin Diaz (rd4birds AT bellsouth DOT net) |
| Yellow-rumped Warbler (Setophaga coronata) | 27 Oct 1993; HY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Yellow-rumped Warbler | 10 Oct 1994; HY-F; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Grace's Warbler (Setophaga graciae ) | 28 Jun 2011; U-U; Coconino National Forest, Mogollon Rim, Buck Springs, Coconino Co., AZ; both elongated, mandible off-center | Flickr |
| Wilson's Warbler (Cardellina pusilla) | 4 Sep 1977; AHY-U; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Wilson's Warbler | 4 Oct 2009; HY-M; Keene, NH; crossed | Kate Yard (kate AT aveo DOT org) |
| Yellow-breasted Chat (Icteria virens) | May 1995; ASY-f; CA; maxilla; 6.77mm longer than mandible | Thomas Leeman (VentanaWS AT aol.com) |
| Yellow-breasted Chat | 27 May 1972; AHY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Summer Tanager (Piranga rubra) | 10 Sep 2003; HY-F; Rector, PA; slightly crossed at tip | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Scarlet Tanager (Piranga olivacea) | 13 Jul 1991; HY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Scarlet Tanager | 20 Jul 1991; HY-F; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Eastern Towhee (Pipilo erythrophthalmus) | 20 Oct 1974; HY-F; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Scarlet Tanager | 27 Jun 2010; AHY-M; Bucktoe Creek Preserve, Chester Co., PA; crossed at tips; some leucistic feathers as well | Holly Merker on Flickr |
| Eastern Towhee | 21 Sep 2004; HY-F; Newburyport, MA; severely crossed | Brian Johnson, Joppa Flats Banding Station (baidaj AT yahoo.com) |
| Spotted Towhee (Pipilo maculatus) | AHY-M; 12 May 1999; near Pierre, SD | Doug Backlund (Doug.Backlund AT state.sd.us) |
| American Tree Sparrow (Spizella arborea) | IL; experiment involving high air temperatures caused bill deformities | West 1959 |
| Field Sparrow (Spizella pusilla) | 21 Oct 1961; U-U; Rector, PA; slightly crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Field Sparrow | 31 Oct 1987; U-U; Rector, PA; maxilla crossed right | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Field Sparrow | 15 Jun 1997; AHY-M; Rector, PA; maxilla slightly crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Field Sparrow | 15 Jan 2012; AHY-U; Bucktoe Creek reserve Chester Co., PA; maxilla elongated, coarse-looking, pointing upwards | Holly Merker on Flickr |
| Lark Bunting (Calamospiza melanocorys) | 21 Dec 2007; U-F; Yuma Co., CO; maxilla elongated and downcurved | Bill Schmoker (bill.schmoker AT gmail.com) |
| Song Sparrow (Melospiza melodia) | AHY-F, 23 May 2000, Point au Sauble, Lower Green Bay, WI | Andy Paulios (paulat06 AT uwgb.edu) |
| Song Sparrow | 1 Sep 2002; HY-U; Burdett, NY; severely crossed | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Song Sparrow | 2 May 2006 through 7 Oct 2006; AHY-F; Pine Gulch Creek, Palomarin Field Station, Point Reyes Bird Obs.; maxilla crossed right over mandible. Bird was not noted to have crossed bill on first capture for banding, but noted on 3 subsequent recaptures. | Mark Dettling (mdettling AT hotmail DOT com) |
| Lincoln's Sparrow (Melospiza lincolnii) | 8 Oct 1990; HY-U; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Golden-crowned Sparrow (Zonotrichia atricapilla) | AHY-U; 16 Jan 1997; San Francisco, CA; crossed; "overweight" at 41 gr! | Rita Colwell (birding AT ibm.net) |
| White-throated Sparrow (Zonotrichia albicollis) | U-U (not a banded bird); 31 Oct 2001; Tunbridge, VT; severely crossed | Anne Aversa (ataversa AT together.net) |
| White-throated Sparrow | 15 Oct 1971; HY-U; Rector, PA; maxilla long and decurved, slightly crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| White-throated Sparrow, also here | 21 Nov 2006; HY-M; maxilla crossed to right; Spring Creek Meadow, High Park, Toronto, Ontario | Toronto Bird Observatory (tboweb ATsympatico.ca) |
| White-crowned Sparrow Zonotrichia leucophrys | 25 March 2011; AHY-U; near Pritchett, CO; crossed at tip | Flickr |
| Dark-eyed Junco (Junco hyemalis) | 5 Dec 1976; HY-F; Rector, PA; maxilla badly crossed to right, gap of 2.5 mm | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Dark-eyed Junco | 28 Oct 1987; AHY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Dark-eyed Junco | 9 Nov 1997; AHY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Dark-eyed Junco | Photo dated 25 Sep 2010; U-U; Mission, BC, Canada; maxilla deformed and curved to one side | Flickr |
| Northern Cardinal (Cardinalis cardinalis) | AHY-F (not a banded bird); 26 Feb 2003; Marietta, GA; mandible severely elongated | Sam Buehner (stamnit AT earthlink.net) |
| Northern Cardinal | 3 Sep 2003; HY-M; Dearborn, Wayne Co., MI; flange on left side of mandible (spoon-like) | Rouge River Bird Observatory,Julie Craves (jac.rrbo AT gmail.com) |
| Northern Cardinal | 8 Oct 2003; HY-M; Burdett, NY; excessive keratin on maxilla | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Northern Cardinal | Jul-Aug 2004; AHY-F; Carol Stream, IL; maxilla spatulate | Dennis Biagoili (DennyRB AT aol.com) |
| Northern Cardinal | 22 May 2006 and 7 Oct 2006; AHY-F; Maxilla 2/3 length of mandible, and crossed over to the right; Metro Beach Metropark, Macomb Co., MI | Allen Chartier (amazilia1 AT comcast.net) |
| Northern Cardinal | 14 Dec 2010; U-F; Southport, NC; bill appearing to have excessive keratin, maxilla elongated, appearing brittle and flaky, mandible elongated, flaky, curving downward, looks like tip broken off but may have been spatulate at one time. | John Ennis (johnxennis AT bellsouth DOT net) |
| Northern Cardinal | 5 and 22 July 2011; HY-U; Cincinnati, OH; severely crossed | Jane Van Coney (vancon4 AT aol DOT com) |
| Northern Cardinal | 3 July 2012; HY-M; near Ypsilanti, Washtenaw Co., MI; maxilla shortened, mandible elongated and spoon or scoop shaped | Denise Gakle; more photos here. |
| Rose-breasted Grosbeak (Pheucticus ludovicianus) | 9 Sep 1904; AHY-F; Illinois?; maxilla sharply downcurved, eye socket misshapen | Woodruff 1907 |
| Rose-breasted Grosbeak | 8 Aug 2002; HY-M; Burdett, NY; deformed on right side, both maxilla and mandible twisted | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Rose-breasted Grosbeak | 10 Oct 1984; HY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Rose-breasted Grosbeak | 30 Aug 2002; HY-F; Burdett, NY; excessive keratin on maxilla, nearly double normal size | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Rose-breasted Grosbeak | 27 Aug 2003; AHY-F; Burdett, HY; growth on maxilla - appears to be excessive keratin formation | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Rose-breasted Grosbeak | 5 Sep 2003; HY-F; Burdett, NY; deformed bill - both excessive keratin on maxilla and misshapen mandible which opened to the sides in an omega shape | John & Sue Gregoire, Kestrel Haven Avian Migration Obs.,(khmo aT att.net) |
| Yellow Grosbeak (Pheucticus chrysopeplus) | ~27 Jan to 1 May 2006; HY-M; Albuquerque, NM; mandible larger and more massive than maxilla. Image here. May be same bird that appeared in Inyo Co., CA 31 Jul - 2 Aug 2006; image here. Bills looked similar. | |
| Indigo Bunting (Passerina cyanea | ~12 Oct 2009; AHY-F; Fort Morgan, AL; bill crossed (photos hard to determine which is out of alignment) and missing left eye. | Jenn Mizen (jennmizen AT gmail DOT com) |
| Red-winged Blackbird (Agelaius phoeniceus) | July 1992; AHY-M; Ventura Co., CA; mandible split | Jim Greaves (LBVIMAN AT BLACKFOOT.NET) |
| Red-winged Blackbird | SY-M; 25 May 1976, Livingston Co., MI; maxilla a recurved stump | Fialia 1981 |
| Red-winged Blackbird | 1 Jun 1968; SY-M; Rector, PA; tips crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Red-winged Blackbird | 19 Mar 2006; two males, SY?; Rowe Sanctuary, Gibbon, NE; elongated with apparently divergent tips | Sharon Stiteler (sharon AT birdchick.com) |
| Red-winged Blackbird | 19 Mar 2006; male, ASY?; Pojoaque, NM; maxilla greatly elongated and wavy, mandible elongated and downcurved | Chuck Hathcock (hathcock AT lanl.gov) |
| Red-winged Blackbird | Atchison, KS; 26 Feb 2011: ASY-M; maxilla very elongated and very flattened | Todd Goehner (kgoehner AT att DOT net) |
| Red-winged Blackbird | 26 Feb 2007; ASY-M; Kuna, ID; maxilla greatly elongated (4-5 inches) | Neva Black (nevablack AT hotmail DOT com) |
| Red-winged Blackbird | 12 Mar 2013; ASY-M; 2 miles west of Hesston, KS; mandible greatly elongated and somewhat thickened. | Allen Pinkall (pinkallaj AT embarqmail DOT com) |
| Western Meadowlark, (Sturnella neglecta) | Antelope State Park, Davis Co., UT; AHY-U; 8 March 2011; maxilla elongated | Mia McPherson (mm AT onthewingphotography DOT com) |
| Meadowlark sp. (Sturnella magna/neglecta) | Winter 2002; Patagonia, AZ; maxilla and mandible greatly elongaged, especially maxilla | Earle Robinson (birdfoto2 AT aol.com) |
| Rusty Blackbird (Euphagus carolinus) | 24 Apr 1968; AHY-M; Rector, PA; crossed | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Common Grackle (Quiscalus quiscula) | 4 Jun 1967; AHY-M; Rector, PA; severely crossed and deformed maxilla | Powdermill Nature Reserve, Robert S. Mulvihill (mulvipnr AT westol DOT com) |
| Common Grackle | June 2008; grossly elongated, keratinized, deformed and downcurved maxilla; Houston, TX | Flickr |
| Brown-headed Cowbird (Molothrus ater) | 20 Jun 2004; SY-M; Ft. Riley, KS, maxilla crossed over bottom | David Rintoul (drintoul AT ksu.edu) |
| Brown-headed Cowbird | 1 May 2000; AHY-M; Brackettville, Kinney Co., TX; crossed | Kevin Ellison (kellis_6 AT yahoo.co.uk) |
| Brown-headed Cowbird | 4 Aug 2004; HY-U; Ft. Hood, Killeen, TX; severely crossed; specimen at Chicago Field Museum Nat. Hist. | Kevin Ellison (kellis_6 AT yahoo.co.uk) |
| Orchard Oriole (Icterus spurius) | 21 Aug 2005; HY-F; upper mandible shortened from tip, and thickened at base, no crossing; Metro Beach Metropark, Macomb Co., MI (photo available from bander). Cross posted at bill tumor page. | Allen Chartier (amazilia1 AT comcast.net) |
| Baltimore Oriole (Icterus galbula) | HY-U; July 1996; Rensellaerville, NY, crossed | Anthony Hill (Anthony_Hill AT hotmail.com) |
| White-winged Crossbill (Loxia leucoptera) | AHY-U; 11 Feb 1973; Fairbanks, Alaska; maxilla 15.2mm beyond lower | West 1974 |
| Common Redpoll (Carduelis flammea) | 6 Apr 2012; Thompson Falls, MT; maxilla slightly miniaturized | Jim Greaves (lbviman AT blackfoot DOT net) |
| Pine Siskin (Spinus pinus) | 19 Oct 12; U-U; Santa Fe, NM; no maxilla; mandible elongated and frayed looking | Maria Higuara (maria AT higuerapope DOT com |
| American Goldfinch (Carduelis tristis) | HY-M; 28 Dec 2003; Dearborn, MI, mandible elongated, maxilla crossed | Rouge River Bird Observatory,Julie Craves (jac.rrbo AT gmail.com) |
| American Goldfinch | AHY-F; 9 Apr 2007; Walden, Orange Co., NY; very elongated mandible | Mark Eis (markeis AT mac DOT com) |
| American Goldfinch | 17 Aug 2007; Lolo, MT; maxilla appears to have been put through a shredder | Jeanne Elliott (jeanne.elliott AT bresnet DOT net) |
| American Goldfinch | 20 April 2008; AHY-F; near St. Ignitius, Montana; very slightly shortened maxilla; bird also has patches of white feathers | Eugene Beckes via Judy Hoy (bjhoy AT localnet DOT com) |
| American Goldfinch | April 2008; AHY/ASY-M; near St. Ignitius, Montana; shortened maxilla | Eugene Beckes via Judy Hoy (bjhoy AT localnet DOT com) |
| American Goldfinch | 20 Oct 2011; U-F; Richland, MI; extremely elongated and downturned maxilla | Reported on MLive news web site |
| Evening Grosbeak (Coccothraustes verspertinus) | Boise, ID; mandible curved to left | Al Larson (allarson AT micron.net) |
| House Sparrow (Passer domesticus) | Cuyahoga, Co., OH; July 2004; male with hugely elongated maxilla, curved down | Maureen McEneryu |
| House Sparrow | 23 Sep to at least 14 Oct 2006; Potomac, MD; entire bill greatly enlarged | via Birder's World forum |
| House Sparrow | approx fall 2001; maxilla curved down | Flickr |
| House Sparrow | Ohio; 17 Sep 2004; maxilla elongated and scoop shaped | Becky Stanton |
| House Sparrow | Photo labeled 25 Apr 10; southern NV; tips crossed | Randall Bruce on Flickr |
| Brown-headed Cowbird | 19 Aug 2011; AHY-M; Boothville, Plaquemines Parish, LA; maxilla extremely elongated and downcurved | Devin Bosler on Flickr |
| House Sparrow | 20 Aug 2010; U-U; Dallas, TX; maxilla nearly absent, mandible grossly enlarged and scoop-shaped | David Flores on Flickr |
Maxilla = Top, Mandible = Bottom.
Literature Cited
Anon. 1999. Vermont Institute of Natural Science, Atlantic Flyway review: northeast coastal region 1 — Fall 1998. N. Amer. Bird Bander 24:54-55.
Fiala, K.L. 1981. Survival of a demaxillate Red-winged Blackbird. Wilson Bulletin 93:563-565.
Green, D. S. 1969. Bill deformity in Clark’s Nutcracker. Blue Jay 27:36.
Eltzroth. E. 1996. Sialia 18:3-4.
Ferreira de Vasconcelos, M. and M. Rodrigues. 2006. Bill deformity in a White-winged Becard (Aves: Subsocines: Tityridae) from Minas Gerais, Brazil. Revista Brasileira de Ornitologia 14:165-166.
Kinch, B. 1998. Deformed chickadee. Ontario Birds 16:45-46.
Small, M. F., & C. L. Pruett. 1998. Rhamphothecal hyperkeratosis in a Bronzed Cowbird. Bull. Texas Ornithol. Soc. 31: 27–29.
Sogge, M. K. and E. H. Paxton. 2000. A summary of observed physical deformities in the Willow Flycatcher: 1996-2000. U.S.G.S. Forest and Rangeland Ecosystem Science Center, Colorado Plateau Field Station, Flagstaff, AZ.
Sperry, D, D. Cimprich, and J. Marquess. 2007. Beak deformity in the endangered Black-capped Vireo. N. Amer. Bird Bander 32: 1-3.
Speirs, J.M. and M. Wilson. 1994. Blue Jay with “crossed” bill. N. Amer. Bird Bander 19:100.
Van Hemert, C. R. 2007. Alaskan Birds at Risk: Widespread Beak Deformities in Resident Species (pdf). Birding 39 (5):48-55.
West, G.C. 1959. Effects of high air temperature on the bill and claw keratin structures of the tree sparrow. Auk 76:534-537.
—–. 1974. Abnormal bill of a White-winged Crossbill. Auk 91:624-626.
Woodruff, F. M. 1907. Malformed bill of Rose-breasted Grosbeak. Auk 24:220-221.
See also the abstract of a paper presented at a 2008 ornithological meeting: The Mystery of the Long-bill Syndrome by researchers at the USGS Alaska Science Center.